BITE BACK - Sonar Strandings

Written by staff reporter Thursday, 04 September 2008 00:00

Photo: Tim Bain/BDMLR

While there have been no definite conclusions as to the cause of this stranding, the fact that the Navy’s statement – that the only recent activity had been the use of a low-powered sea bed scanner – was later shown to be false has inevitably raised questions. Certain peculiar features – animals stranded themselves over a 15km-wide area, and there was a large number of other dolphins crowded into the bay – suggest that a single event frightened the animals into the river system.

Information from the Ministry of Defence has been sparse and contradictory, but certainly there was a major naval exercise going on involving a number of countries. While the Navy denies that it was using low-frequency sonar, it has so far refused to disclose whether mid-range frequency sonar, which has the greatest affect on cetaceans, was in use. It has also come to light that an exercise involving a Merlin helicopter equipped with a mid-frequency sonar dipper, which is lowered into the water where it emits pulses of sound beyond human hearing, was in use further up the coast some days earlier.

Both the British and US navies have been reluctant to admit that the use of sonar, and in particular their long-range active systems, has an adverse affect on marine life. However, the scientific committee of the International Whaling Commission has stated that the evidence that active sonar leads to strandings ‘is very convincing and appears overwhelming’.

In the US Navy’s Low Frequency Active system, each speaker can produce 215 decibels, equivalent to a twin-engine fighter during take-off. Mid-frequency systems can put out more than 235 decibels, similar to the Saturn V rocket at launch. And these are going into water, which transmits sound much quicker and further than air. Even 480km from the source, sound levels can approach 140 decibels – well above the US Navy’s safety limit for humans and 100 times more intense than the level known to alter the behaviour of large whales.

In 2000, a mass stranding of beached whales – with many of them showing physical trauma, including bleeding around the brain, ears and other tissues – occurred in the Bahamas and the local population of Cuvier’s beaked whales disappeared completely. A government investigation showed that a US naval exercise, using mid-range sonar, was directly responsible. In February this year, the dead bodies of pilot and Cuvier’s beaked whales started appearing on the west coast of Scotland; more than 50 whales have so far washed ashore. It seems clear from the studies that all these whales were killed by a single event, although both the British Navy and the Russians, who had ships operating in the area at the time, deny being the cause.

What is clear is that strandings such as we saw in Cornwall are likely to be just the tip of the iceberg. Much bigger coastal strandings do occur – such as the 400 bottlenose dolphins that washed ashore in Tanzania one afternoon, and were linked to a US Navy counter-terrorism operation on Africa’s east coast – but the vast majority of affected whales and dolphins will simply die out at sea and disappear.

The government needs thoroughly investigate the Cornwall strandings to establish if there was a link with naval activity. If such a connection is shown, pressure can be brought on the Navy to limit the affects on marine life of long-range sonar. Email Hilary Benn, the Secretary of State responsible for such matters, on This e-mail address is being protected from spambots. You need JavaScript enabled to view it